Bird Communities along a Montane Sere: Community Structure and Energetics

We examined 11 of 24 ecosystem attributes that Odum (1969) proposed would change during succession in avian communities in meadow, aspen, fir, and spruce forests in northern Utah and southern Idaho. A total of 71 bird species was observed during the 30-month study, of which 43 were known to breed. Yearly energetic relationships were calculated for the breeding bird populations using an avian community energetics model. In the different avian communities, the ratios of annual secondary production/community respiration, secondary production/biomass present, and secondary production/ consumption all tended to decrease with increasing plant succession; biomass present/ unit energy flow tended to increase. All of these trends are consistent with those postulated by Odum for the entire ecosystem. These energetics ratios differed in 1977 from those in 1976 and 1978 due to a severe drought. They also fluctuated greatly during the course of a year. Avian species diversity was highest in the preclimax fir forest during the breeding season and fluctuated widely in the nonbreeding season. Species equitability tended to be relatively high in all avian communities, although it was slightly lower during the nonbreeding season. No trends were found in male body sizes, mean clutch size, and mean length of incubation period (a crude measure of parental investment). Thus, for the bird communities, we reject the postulated trends of increased species diversity, equitability, and organism size in the climax, quantity to quality production, and r- to K-selection. During the drought of 1977 the spruce avifauna appeared more stable, so we cannot reject Odum\u27s hypothesized trend of increased stability in the climax. We conclude that the vegetational characteristics of a given sere will in most cases determine the avian population response along that sere; this in turn will influence the correspondence of the avian communities to Odum\u27s postulates. Incorporating these avian results with other studies within our subalpine sere, some of Odum\u27s hypothesized trends are supported while others are not, suggesting that successional relationships are more complicated than would follow from Odum\u27s relatively simple model